[Pd] Serial port out

[Steffen]

On 16/11/2006, at 23.53, Chuckk Hubbard wrote:

> My plan was to send PWM from my serial port, then use a low pass  
> filter to obtain DC to
> control a Moog synthesizer's pitch.

I don't quite understand how a PWM'ed signal put through a low pass  
filter can give a voltage controlling signal. Care to explain? I'm  
not even sure how to make the PWM signal at all - will it only be  
using one pin? I might be daft.

I thought the easiest way to obtain such a signal from a serial port,  
was to make a D/A converter fx with a transistor construction  
(couldn't just find a diagram on the internet), such that each bit  
sent to the port would translate to a DC signal. I know the precision  
of the values might be sloppy and that there will only be 2^{# of  
data pins on the port} different control values to mess with - but  
still?

I read about it in Delton T. Horns Music Synthesizers: A Manual of  
Design and Construction, if i recall correct, where the author  
suggested to use a S/H in connection with such a converter to save  
CPU power (when one wanted to keep a given CV for a period of time  
(faster then the port)).


> Christian Klippel, however, has kindly offered to create a USB->CV  
> adaptor for me, something others have suggested but which has  
> proven too confusing for me.

That's very nice. I'd really love to make such a lil' donkey myself.